The Justice Department is investigating whether a prominent billionaire bribed a Middle Eastern government, according to court filings in Florida.

Harry Sargeant III, a well-connected energy magnate, was once the finance chairman of the Florida Republican Party and a principal supplier of fuel to U.S. forces in Iraq. In April, msnbc.com reported that his Florida-based oil trading business, International Oil Trading Co., may have secured an exclusive license to ship the fuel through Jordan — as defense contracts required — by paying off the country's government.

Unearthed emails from 2007 showed Marty Martin, a manager at the oil company and former head of the CIA's Osama bin Laden unit, wiring $9 million to an account "designated" for the chief of the Jordanian intelligence agency. The Jordanian king's brother-in-law, Mohammad al-Saleh, has called the money a kickback, and he is suing Sargeant and a partner, Mustafa Abu-Naba'a, in Palm Beach, Fla., for purportedly cutting him out of a one-third share in the oil company.

In new court filings, al-Saleh's lawyers allege that the $9 million wire is the focus of a pending grand jury investigation by the Justice Department into possible violations of the Foreign Corrupt Practices Act. And the Jordanian government has launched its own investigation of Gen. Mohammad Dahabi — ex-chief of the country's intelligence agency — for his involvement in the wire transfer, the filings state.

Sargeant's lawyers told msnbc.com in April that the $9 million was payment to a quasi-government subcontractor in Jordan and denied wrongdoing. But al-Saleh's lawyers contend in court filings that Sargeant's side has offered contradictory explanations for the transfer, with Sargeant and Martin claiming in sworn depositions that it was a payment to al-Saleh.

Asked about the grand jury investigation, Ron Uscher, a lawyer for Sargeant, said, "You shouldn't know about that," but he then claimed to know nothing of it and declined further comment. Another lawyer for Sargeant did not respond to repeated inquiries, and al-Saleh's lawyers declined to comment. In a deposition, Abu Naba'a, a Dominican businessman, acknowledged that he had been contacted in recent months by Justice Department investigators. The Justice Department did not respond to inquiries.

Sargeant has been under almost-continuous investigation by government branches since 2008, when a congressional committee excoriated his oil firm for "engaging in the worst form of war profiteering." The committee found that Sargeant used monopoly power to overcharge the Defense Department for fuel starting in 2004, gouging taxpayers out of hundreds of millions of dollars while enriching himself. A subsequent Pentagon audit found this year that Sargeant was overpaid by as much as $200 million on a series of fuel contracts worth more than $2 billion.

But msnbc.com has learned that Sargeant is now suing the Pentagon before the Armed Services Board of Contract Appeals for $75 million, claiming that he was underpaid. The case is pending.